Cut the pork (or other meat) across the grain into small, thin strips.

In a large, heavy skillet (cast iron works best) or in a wok, heat the oil over high heat until it is smoking hot. Add the celery and onion and cook briskly, stirring and tossing furiously, for about 2 minutes.

Add the pork, mushrooms, and pepper and continue cooking over high heat, tossing and stirring all the while, for about 3 minutes more, until the meat is cooked through.

Add the bean sprouts and cook, tossing for 1 minute.

Quickly stir the broth, cornstarch, and soy sauce together until blended. Add to the other ingredients along with the green onion, and cook for 1 minute more, until thickened.

Season with salt and pepper to taste, and serve over rice.